1. Field of the Invention
This invention broadly relates to methods and articles used in the course of orthodontic treatment. More particularly, the present invention relates to methods and articles used in conjunction with orthodontic appliances that are bonded directly to the patient's teeth.
2. Description of the Related Art
Orthodontic treatment involves movement of a dental patient's teeth to improved positions in proper alignment with each other. Orthodontic treatment can greatly enhance the patient's facial appearance, especially in regions near the front of the oral cavity. Orthodontic treatment can also improve the function of the teeth so that the opposing teeth work better with each other during mastication.
One type of common orthodontic treatment includes the use of a set of tiny appliances known as brackets. Each bracket has a slot and is affixed to one of the patient's anterior, cuspid or bicuspid teeth. Conventionally, a thin, resilient metallic archwire is received in the slots of the brackets and forms a track to guide movement of the teeth to desired positions. Ends of the archwire are often received in buccal tube appliances that are affixed to the patient's molar teeth.
Another type of common orthodontic treatment system involves a series of custom-made plastic positioning trays such as the “Invisalign” brand trays sold by Align Technology of Santa Clara, Calif. Each tray is made to move the teeth a relatively small, incremental distance toward desired final positions. The trays are made of a plastic material with sufficient resiliency to urge the teeth toward positions defined by the tray when the tray is relaxed.
However, plastic positioning trays sometimes have difficulty applying certain types of forces to teeth. For example, it is difficult for conventional positioning trays to apply a force in an extrusive direction (i.e., moving a tooth in a direction toward its outer tip). Moreover, the amount of force applied to the teeth is limited by the resiliency characteristics of the plastic material, which in general is somewhat less than can be applied to the teeth by the use of brackets and archwires.
Some orthodontic practitioners have used a “combination” treatment plan, wherein the patient is provided with a series of the plastic positioning trays at the beginning stages of treatment. Subsequently, and after the teeth are located closer to desired final positions, the use of the trays is discontinued and replaced by brackets and archwires. It is often thought that the use of brackets and archwires in the final stages of treatment provides a better result in terms of moving the teeth to exact desired positions at the conclusion of treatment.
It has also been proposed to use bonded orthodontic appliances simultaneously with plastic positioning trays. For example, U.S. Pat. Nos. 6,309,215 and 6,705,863 describe plastic positioning trays having receptacles for removably receiving appliances that are directly bonded to the patient's teeth. The bonded appliances can function as a handle to facilitate the transmission of force between the teeth and the positioning tray.
Regardless of whether or not orthodontic appliances such as brackets are used alone or in combination with a repositioning tray, it is desirable that the appliances debond easily and predictably from the teeth at the conclusion of treatment. Metal brackets, for example, are typically debonded from teeth by using a peeling or prying motion. An improved ceramic bracket having a debonding channel is described in U.S. Pat. Nos. 5,439,379 and 5,366,372, and the bracket is debonded by pivoting sections of the bracket toward each other.
However, it is also important to ensure that the orthodontic brackets do not spontaneously debond from the tooth before the practitioner intends to remove the brackets. If, for example, a bracket detaches from the tooth prior to the conclusion of treatment, the detached bracket must normally be re-bonded or replaced with a new bracket in order to resume the course of treatment. As can be appreciated, premature debonding of orthodontic brackets represents a significant nuisance to both the orthodontist and the patient that is best avoided if at all possible.